Synthesis, Characterization, and Application of Chiral Ionic Liquids and Their Polymers in Micellar Electrokinetic Chromatography
作者:Syed Asad Ali Rizvi、Shahab A. Shamsi
DOI:10.1021/ac060878u
日期:2006.10.1
Two amino acid-derived (leucinol and N-methylpyrrolidinol) chiral ionic liquids are synthesized and characterized in both monomeric and polymeric forms. Leucinol-based chiral cationic surfactant is a room-temperature ionic liquid, and pyrrolidinol-based chiral cationic surfactant melts at 30−35 °C to form an ionic liquid (IL). The monomeric and polymeric ILs are thoroughly characterized to determine critical micelle concentration, aggregation number, polarity, optical rotation, and partial specific volume. Herein, we present the first enantioseparation using chiral IL as a pseudostationary phase in capillary electrophoresis. Chiral separation of two acidic analytes, (±)-α-bromophenylacetic acid and (±)-2-(2-chlorophenoxy)propanoic acid (±)-(2-PPA) can be achieved with both monomers and polymers of undecenoxycarbonyl-l-pryrrolidinol bromide (l-UCPB) and undecenoxycarbonyl-l-leucinol bromide (l-UCLB) at 25 mM surfactant concentration using phosphate buffer at pH 7.50. The chiral recognition seems to be facilitated by the extent of interaction of the acidic analytes with the cationic headgroup of chiral selectors. Polysodium N-undecenoxycarbonyl-l-leucine sulfate (poly-l-SUCLS) and polysodium N-undecenoxycarbonyl-l-leucinate (poly-l-SUCL) were compared at high and low pH for the enantioseparation of (±)-(2-PPA). At pH 7.5, poly-l-SUCLS, poly-l-SUCL, and (±)-(2-PPA) are negatively charged resulting in no enantioseparation. However, chiral separation was observed for (±)-(2-PPA) using poly-l-SUCLS at low pH (pH 2.00) at which the analyte is neutral. The comparison of chiral separation of anionic and cationic surfactants demonstrates that the electrostatic interaction between the acidic analyte and cationic micelle plays a profound role in enantioseparation.
合成了两种氨基酸衍生的手性离子液体(亮氨醇和 N-甲基吡咯烷醇),并以单体和聚合物形式对其进行了表征。基于亮氨酸醇的手性阳离子表面活性剂是一种室温离子液体,而基于吡咯烷醇的手性阳离子表面活性剂在 30-35 °C 下熔化形成离子液体 (IL)。我们对单体和聚合物离子液体进行了全面的表征,以确定临界胶束浓度、聚集数、极性、光学旋转和部分比容。在此,我们首次在毛细管电泳中使用手性离子液体作为假固定相进行对映体分离。使用 pH 值为 7.50 的磷酸盐缓冲液,在 25 mM 的表面活性剂浓度下,使用十一烯氧羰基-l-丙烯基溴化锂(l-UCPB)和十一烯氧羰基-l-亮氨酸溴化锂(l-UCLB)的单体和聚合物,可以实现两种酸性分析物--(±)-α-溴苯乙酸和(±)-2-(2-氯苯氧基)丙酸(±)-(2-PPA)的手性分离。酸性分析物与手性选择剂阳离子头基的相互作用程度似乎有助于手性识别。比较了 N-十一碳氧羰基-亮氨酸硫酸钠(poly-l-SUCLS)和 N-十一碳氧羰基-亮氨酸聚钠(poly-l-SUCL)在高pH值和低pH值下对(±)-(2-PPA)进行对映体分离的效果。在 pH 值为 7.5 时,poly-l-SUCLS、poly-l-SUCL 和 (±)-(2-PPA) 均带负电荷,因此无法进行对映体分离。然而,在分析物呈中性的低 pH 值(pH 值为 2.00)条件下,使用聚-l-SUCLS 可观察到 (±)-(2-PPA) 的手性分离。阴离子和阳离子表面活性剂的手性分离比较表明,酸性分析物和阳离子胶束之间的静电相互作用在手性分离中起着重要作用。